The present invention relates to a valve for handling high pressure fluids. The invention will be explained in connection with a valve for use in the oil and gas producing industry, and particularly for use at the well head.
It is common at well heads to provide chokes, sometimes called "beans" which are single point restriction devices employed to effect a high pressure drop in connection with gases, liquids and fluids, which exit the well in dirty condition, i.e., not infrequently having some entrained granular materials.
Obviously a single point restriction results in considerable wear even with tungsten carbide trim. It is not uncommon to simply retrim the high pressure choke and put it back in use, at substantial expense.
On the other hand, when handling clean fluids (liquids and/or gases) rather than resorting to single point restriction devices, it is common practice to utilize multi-staging to obtain a pressure drop.
These multi-stage valves are generally of two kinds, the first being an axial flow and the second being radial flow.
The U.S. Pat. No. 3,485,474 to Baumann shows a typical multi-stage valve of the axial flow type, in which the ribs or protrusions 27 of progressively increasing size are provided on an axially disposed shaft. The ribs are disposed in a cooperative relationship with recesses formed in the body, to provide plural throttling stations. At each station there are plural turns or elbows, where the fluid path includes an inner axial leg, followed by an outward radial leg, in turn followed by an outer axial leg, followed by an inward radial leg.
The shaft can be adjusted axially. This is said to vary, at each station, the depth H of the path of the outward radial leg, while maintaining constant the depth W of the path at the outer axial leg. However, whatever change in flow path depth that occurs in the outward radial leg, the opposite change in flow path depth occurs in the inward radial leg, at each of the throttling stations. Thus, only at the midpositions of the ribs or protrusions are the depths of the two radial paths of a station equal.
In FIG. 4 of Baumann, protrusions are formed in an intermeshing pattern to provide grooves, so that the fluid is again forced to change directions with the resultant loss in pressure while passing from one circular groove to the next.
Typical of the second type of valve are the valves shown in patents such as Bates Re. No. 31,105 and U.S. Pat. No. 3,984,716 to Barb in which multiple plates are provided, with fluid flowing radially between opposed plates, there being a plunger to select how many of the annular paths are to be used.
The U.S. Pat. No. 4,205,696 to Gongwer shows a throttling valve in which the fluid flows radially between multiple plates, and wherein the spacing between the plates can be varied by axially moving the plates relative to one another, until the seating of certain heads of alternate plates on seating surfaces provided by adjacent plates.
Reference is also made to the Canadian Pat. No. 963,356, to A. Sultan issued Feb. 25, 1975. This patent does not actually show multiple staging, but is essentially a single stage pressure drop valve for use in handling water in cooled nuclear reactors. However, two concentric annular lands are arranged to intermesh as the closure member approaches the port member to define a flow path which has several changes of direction of flow, sudden enlargements and contractions of flow area, thereby said to produce velocity head losses at low rates of flow through the valve.
Multi-staging valves have been considered unsuitable for use at well heads, because the multi-staging valves frequently have restricted passages and/or orifices which can quickly become clogged with the dirt and grit entrained in the well head fluids.
The design requirements for an effective choke in oil field operations are formidable. There are a multiplicity of applications in any given oil field and every well is different, yet the operators desire one type of control device. Also, the nature of the problem changes with maturing of fields. Further, fluid can and does carry sand and large particles which break from the producing formations, with the result at the choke of erosion and plugging. Chokes must have wide control rangeability. They should be corrosion-resistant, including conformance to material requirements for H2S handling. They need to handle liquids, gases, or mixtures thereof equally well, and to be cavitation-free as well as noise-free.
It is a primary purpose of the present invention to provide a valve capable of meeting the above requirements, and which does so by means of pressure reduction in multiple stages, but in a single radial flow path, wherein the valve is so configured and designed that it has a self-cleaning feature enabling it to handle dirty fluids without becoming clogged.
My valve has a pair of opposed plates with interdigitated annular elements or teeth to form a single generally sinuous radial flow path wherein the volume of the annular zones increases progressively from the center outward to provide for a staging of the pressure drop, and wherein the elements have angular faces, so that as the plates are moved toward and away from one another, the depth or thickness of the sinuous path is varied to thereby vary the flow through the valve under controlled conditions.
A further object is to provide a valve as just described which is so constructed that the depth of the various legs of the flow path are varied equally in order to maintain cross section continuity, and so that the depth of the restricted passages is directly proportional to adjustment or lift.
A still further object is to provide a valve wherein the angles of the teeth are varied to attain a progressive change in the depths of the flow path legs.
It is a primary object of the invention to provide a high pressure multiple stage valve which can handle dirty fluids and which achieves multiple staging by a unique configuration and arrangement of the parts.